Trunked RF communication systems are known in the art. Such systems operate by allocating a limited number of frequency resources amongst a number of communication units (as used herein, "communication units" refers to two-way radios, including mobile radios, portable radios, and fixed location radios). To facilitate this allocation, such systems typically provide system control information, either in a dedicated control channel or control slot, or in a distributed manner, by including the control information subaudibly with message information such as voice signals.
In some applications, system resources are best utilized when a communication unit has the capability of monitoring system control information at all times. Such capability allows a communication unit to respond quickly to changing resource needs or other situations. In a communication system where messages are transmitted from a central to the communication units via a TDM format, and where communications from the communication units to the cental are in the form of continuous transmission signals, such capability is difficult to provide in a cost effective and satisfactory manner.